func SignPKCS1v15(random io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) ([]byte, error) {
	// pkcs1v15ConstructEM is called before boring.SignRSAPKCS1v15 to return
	// consistent errors, including ErrMessageTooLong.
	em, err := pkcs1v15ConstructEM(&priv.PublicKey, hash, hashed)
	if err != nil {
		return nil, err
	}

	if boring.Enabled {
		bkey, err := boringPrivateKey(priv)